Driving while talking on the phone, even with a hands-free device, is generally not considered safe. When a driver holds a conversation with a passenger in the car, that passenger generally reacts to the surroundings the same way the driver does. He/she will warn the driver of upcoming hazards and will be quiet during emergency situations. In addition, the passenger may see blind spots that the driver may not notice. On the other hand, when holding a conversation with someone on a hands-free mobile phone, the caller often ignores the driver's surroundings and continues to talk during driving emergencies. Even worse, the caller may reprimand the driver for not talking when the driver is trying to navigate a dangerous maneuver requiring concentration.